As cuttings are near the surface and seldom at greater depths than 100 feet, it is hardly possible to know the angle at which a rock dips or whether there are faults and fissures in it, unless an examination is made upon the site, and this notwithstanding the geological character may be thoroughly understood. Local conditions may cause peculiarities which no law can determine, and although at considerable depths, deeper than railway or any works with the exception of well-sinking and mining are likely to reach, the nature of the earth is accurately ascertained; the surface soil may be in almost every conceivable variety, and also so dislocated, denuded and rearranged, that usually horizontal strata may be nearly vertical. Its character may be accurately known, but the lie of the surface beds or dip of the upper strata, or the order of supraposition cannot be invariably absolutely established; for instance, when crevasses, fissures and veins are frequent in earth upheaved and disintegrated by volcanic action, earthquakes and other disturbing causes, as in parts of South America, Japan, and other eastern countries, Italy, the Tyrol, Spain, &c., &c., slips of earthwork are to be expected, and the soil is likely to be much inclined, full of faults and probably water-bearing seams. Under the comprehensive name of rock is usually included any earth from the hardest mass to be found to that which will crumble in the hand, as soft sandstone rock. The chief absorbent rocks with which engineers have to do are the limestones, sandstones, chalk, and clay rocks. Rock may also be simple or present the appearance of being homogeneous, or it may be a mass of different substances, be flat bedded, have open or close joints, and be what is called— Solid rock. Hard rock. Dense, or compact, rock. Loose rock. Rock in loose layers. Loose rock with cavities, caverns, and pot-holes of various earths. Fissured rock. Friable rock. Indurated earth liable to be disintegrated by atmospheric influences. Decomposed rock. Rotten decomposed rock. Or any mass of earth cemented together by a substance, weather-resisting or not, requiring blasting or that can be excavated by means of bars and picks. The slope of repose required may range from overhanging or vertical to that of the earth of which it consists when disintegrated and dissolved; therefore the angle of repose varies considerably, but the following cardinal principles may be followed without fear under ordinary circumstances and conditions. Granite. Quartz, if not fissured, and when little mica is present in it, and most of the igneous rocks, Overhanging, vertical, TO ⅛ to 1. Also porphyry, gneiss, trap, but their stability varies considerably. Compact hard sandstone and limestone and other solid sedimentary rocks producing stone sufficiently hard and weather-resisting that it can be used in construction, Perpendicular, TO ¼ to 1.